Rotator cuff repair is the most common surgical repair performed in the shoulder, with more than 270,000 repairs performed annually in the United States, as of 2006, with that number expected to increase annually with concurrent increase in the aging population. Advances in rotator cuff repair technique have focused principally on transition from open repair, to mini-open repair, and more recently to fully arthroscopic repair. Moreover, advances have been made in suture patterns or arthroscopic repairs to better recreate the natural footprint insertion of the rotator cuff to improve time-zero mechanical properties, and in hopes of improving the healing rates.
In spite of improvements in surgical technique, healing rates as evidenced by postoperative ultrasound or MRI have varied widely, ranging from 91% healing rates in small tears to healing rates of only 10% in the largest tears. It is believed that healing rates are low due to the inadequate re-creation of the natural anatomic bone-tendon interface.
Various techniques have been employed to improve interface healing, including mesenchymal stem cells, xenograft, allograft, and acellular nanofiber scaffolds. Advances in nanofiber technology may hold promise in improving the bone-tissue interface healing of many soft tissue injuries, and have several advantages over other proposed methods. Issues of procurement, scalability, ease of use, and integration with currently performed surgical repair methods favor the nanofiber scaffolds. As noted in Inui et al. (“Regeneration of Rotator Cuff Tear Using Electrospun Poly (D,L-Lactide-Co-Glycolide) Scaffolds in a Rabbit Model”), The Journal of Arthroscopic and Related Surgery, Vol. 28, No. 12 (December), 2012; pp. 1790-1799, nanofiber size can range up to about 14 μm in the orthopedic field.
Usage of acellular augmentation devices have been evaluated in animal models, demonstrating safety to the animal and effectiveness in improving the soft tissue healing. Yokoya et al. (“Tendon-Bone Insertion Repair and Regeneration Using Polyglycolic Acid Sheet in the Rabbit Rotator Cuff Injury Model”, American Journal of Sports Medicine, Vol. 36, no. 7, pp 1298-1309, 2008) used a polyglycolic acid (PGA) sheet to augment rotator cuff repairs of infraspinatus tendons in Japanese white rabbits, showing histological improvement in fibrocartilage layering and a slight improvement in tensile strength when compared to control tendons. Funakoshi et al. (“Rotator Cuff Regeneration Using Chitin Fabric as an Acellular Matrix”, Journal of Shoulder and Elbow Surgery, Vol. 15, No. 1, pp. 112-118, 2006) demonstrated increased fibroblast presence and collagen formation when synthetic extracellular matrix was surgically applied to rotator cuff tears in Japanese white rabbits. MacGillivray et al. (“Biomechanical Evaluation of a Rotator Cuff Defect Model Augmented with a Bioresorbable Scaffold in Goats”, Journal of Shoulder and Elbow Surgery, Vol. 15, No. 5, pp. 639-644, 2006) used polylactic acid patches in goats, showing safety to the animal but minimal difference between the treated and control groups. A similar experiment using a woven poly-L-lactide device was performed by Derwin et al. (“Rotator Cuff Repair Augmentation in a Canine Model with Use of a Woven Poly-L-Lactide Device”, Journal of Bone and Joint Surgery A, Vol. 91, No. 5, pp. 1159-1171, 2009) in a dog model. A portion of each infraspinatus tendon was removed from the rotator cuff and then repaired in both shoulders. In one shoulder, a woven poly-L-lactide device was placed over the repair. In the other shoulder, the repair was left unaugmented. The augmented rotator cuff repair resulted in fewer tendon retractions, greater strength, and increased stiffness when compared to the contralateral untreated rotator cuff repairs.
In an attempt to improve the healing of the tissue-bone interface, acellular nanofiber scaffolds have been studied. Nanofiber scaffolds are typically made from materials with well-known biologic properties. For example, poly-lactide-co-glycolide (PLGA) is a material commonly used in absorbable sutures and medical devices. PLGA can be fashioned via electrospinning into nanofiber sheets, which in turn can be interposed between a torn tendon and the underlying bone attachment site during surgical tissue repair. Additionally, other polymers that are non-absorbable have been used as nanofiber scaffolds as well. When used in this manner it should be noted that the nanofiber is not acting as a structural graft under tension. The interposed fibers are used only as a scaffold to support ingrowth of host cells.
Moffat et al (“Novel Nanofiber-Based Scaffold for Rotator Cuff Repair and Augmentation”, Tissue Eng Part A, Vol. 14, pp. 1-12, 2008) used an in vivo model to study the potential for an aligned nanofiber sheet to promote fibroblast formation and improved mechanical properties. They found that “mechanical properties of the aligned nanofiber scaffolds were significantly higher than those of the unaligned, and although the scaffolds degraded in vitro, physiologically relevant mechanical properties were maintained. These observations demonstrate the potential of the PLGA nanofiber-based scaffold system for functional rotator cuff repair. Moreover, nanofiber organization has a profound effect on cellular response and matrix properties, and it is a critical parameter for scaffold design.” Some controversy exists over the best nanofiber architecture: monophasic, biphasic, or even triphasic.
Implantation of sheets of material as studied by Moffat, Derwin, MacGillivray, Funakoshi, and others requires an open surgical procedure. The current standard-of-care for rotator cuff repair is an arthroscopic procedure, growing from less than ten percent of all rotator cuff repairs in 1996 to almost sixty percent of all rotator cuff repairs in 2006. The trend has continued in the past 6 years, with current estimates suggesting that greater than 85% of rotator cuff repairs are performed arthroscopically. Further improvements to the procedure that are potentially offered by devices and/or materials as described by Moffat must be compatible with arthroscopic implantation methods in order to be widely accepted.
Rotator cuff repair surgery has evolved from predominately being performed with an open procedure to an arthroscopic procedure during the past 15 years. The current state-of-the art arthroscopic procedure generally utilizes one of the following approaches:
a) as shown in FIG. 1, a single row of suture anchors 1 lying underneath the rotator cuff tendon 2 with sutures passed up through the tendon and securely tied to anchor the tendon to the bone 3;
b) as shown in FIG. 2, a double row of suture anchors 1 lying underneath the rotator cuff tendon 2 with sutures passed up through the tendon and securely tied to anchor the tendon to the bone;
c) as shown in FIG. 3, a single row of suture anchors 1 lying underneath the rotator cuff tendon 2 with sutures passed up through the tendon, securely tied, with suture from knots extending laterally over the tendon and secured to the bone 3 with a knotless suture anchor 4 that is outside the margin of the tendon.
There are no prospective, randomized published studies that show a difference in outcome between the three procedure groups listed above and depicted in FIGS. 1-3, and in spite of improvements in surgical technique, failure rates (defined as the tendon not healing to the bone) as evidenced by postoperative ultrasound or MRI have varied widely, range from 9% in small tears, to 90% in the largest tears. It is believed that failure to heal is due to the inadequate re-creation of the natural anatomic bone-tendon interface.
Various techniques have been employed to improve interface healing, including mesenchymal stem cells, xenografts, allografts, and acellular nanofiber scaffolds. Advances in nanofiber technology may hold promise in improving the bone-tissue interface healing of many soft tissue injuries, and have several advantages over other proposed methods. Issues of procurement, scalability, ease of use, and integration with currently performed surgical repair methods favor the nanofiber scaffolds.
A product that combines the current arthroscopically-placed suture anchor implants with a nanofiber scaffold, as disclosed and described herein, will allow the surgeon to repair the rotator cuff using current arthroscopic methods.